What do such sciences as GNI physiology and psychology have in common, and what is their difference?

Both study behavior. The first from the point of view of physiology, the second from the point of view of the state of mind.

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.